Thermal control device



July 10, 1956 w. R. POLYE 2,754,472

' THERMAL CONTROL DEVICE Filed March 10, 1950 RESISTANCE I l TIME INVENTOR.

W/LL/AM R. POLVE BY THERMAL CONTROL DEVICE William R. Polye, River Edge, N. J., assignor to Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application March 10, 1950, Serial No. 148,874

4 Claims. (Cl. 323-69) The invention relates to control devices and more particularly to a sealed tube type of thermal control device.

The main object of the present invention is to provide a novel thermal control device which produces a signal corresponding to the rate of change of current in a circult associated with the device.

The invention contemplates a pair of impedances of substantially equal resistance with uniform current flow when heated to the steady state. The resistance of one of the impedances increases more rapidly with step changes in current than the resistance of the other impedance. The impedances may be connected in a bridge circuit so that the resulting output of the circuit with step changes in current is proportional to the difference in resistance of the impedances.

The foregoing and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawing wherein one embodiment of the invention is illustrated. It is to be expressly understood, however, that the drawing is for the purposes of illustration and description only, and is not to be construed as defining the limits of the invention.

In the drawing,

Figure 1 is a perspective view of a thermal control device constructed according to the invention.

Figure 2 is a schematic diagram showing the device connected in a control circuit; and

Figure 3 shows curves illustrating the resistance of the resistors in Figure 2 plotted against time during a step change in current flowing through the resistors and a curve corresponding to the output of the circuit of Figure 2.

Referring now to the drawing for a more detailed description of the thermal control device of the present invention, the device is shown in Figure 1 as comprising a tube having an evacuated glass envelope 1 with a base 3. Pins 5, 7, 9, 11, 13, 15 and 17 are sealed in the base and extend from the envelope for reception in an associated socket (not shown). Pins 7 and 15 extend into the envelope substantially to its opposite end and are secured to mica discs 19, 21. Pins 5, 9, 13 and 17 extend only a short distance into the envelope and are secured to mica disc 21. Discs 19 and 21 engage the walls of the envelope and firmly hold the pins in position within the envelope.

A resistor 23 formed of a straight piece of wire is secured at one end to pin and at its opposite end to a bracket 25 attached to one end of pin 7. A resistor 27 of greater mass than resistor 23 and in the form of a helix is secured at one end to pin 9 and at its opposite end to a bracket 23 attached substantially to the middle of pin 7. Likewise, a resistor 31 corresponding to resistor 23 is attached at one end to pin 13 and at its other end to a bracket 33 secured to one end of pin 15. A helical resistor 35 corresponding to resistor 27 and of greater mass than resistor 31 is attached at one end to pin 17 and at its States Patent opposite end to a bracket 37 secured substantially to the middle of pin 15.

By forming resistors 27 and 35 helically, the adjacent turns of the helix radiate heat to each other so that the effective radiating area of resistors 27 and 35 is substantially the same as the radiating area of resistors 23, 31.

Resistors 23, 27, 31, 35 preferably are formed of nickel wire and have equal temperature coefiicients of resistance so that the resistors are of equal resistance, with uniform current flow when heated to the steady state or equilibrium temperature.

Since the mass of resistors 27, 35 is greater than the mass of resistors 23, 31, with a step increase or step decrease in current, the temperature and resulting resistance of resistors 27, 35 increases or decreases more slowly than the temperature and resulting resistance of resistors 23, 31.

In Figure 2, resistors 23, 27, 31, 35 provide the four arms of a bridge circuit. Pins 5 and 17 are connected together and pins 9 and 13 are connected together. A battery 39 and a switch 41 in series therewith are connected to pins 5, 17 and to pins 9, 13. The output of the circuit is measured at terminals 43 connected to pins 7 and 15..

When a step change in current occurs in the bridge circuit by closing or opening switch 41, resistors 23, 31

will heat or cool more rapidly than resistors 27, 35 and. the resistance of resistors 23, 31, indicated by the curve A. in Figure 3, will change more rapidly than the resistanceof resistors 27, 35, indicated by the curve B in Figure 3, so that a signal corresponding to curve C in Figure 3 willi appear across terminals 43 until the resistors 23, 31, 27,, 35 have attained a steady temperature, whereupon the Upon closing switch 41 at time T 0, resistors 23, 31 require a time T11 and resistors 2'7, 35 require a time T2 to attain a steady signal across terminals 43 will drop to zero.

temperature and resistance. This condition will exist until another step change in current occurs across the bridge circuit.

The device described provides a novel thermal control device which produces a signal corresponding to the rate of change of current in a circuit associated with the device.

Although but one embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. In a device of the kind described, a sealed envelope, a pair of resistors formed of the same material and mounted within said envelope and being of substantially equal resistance with uniform current flow, one of said resistors being in the form of a helix and the other resistor being substantially straight so that one of said resistors changes resistance at a faster rate with step changes in current than said other resistor.

2. in a device of the kind described, an envelope, a plurality of pairs of resistors formed of nickel wire and mounted within said envelope, the resistors of each pair being of substantially equal resistance with uniform cur" rent flow when heated to the steady state, one of said resistors of each pair being in the form of a helix and the other resistor of each pair being substantially straight and of less mass than said heiical resistor so that said straight resistor changes resistance at a faster rate with step changes in current than said helical resistor.

3. In a device of the kind described, an evacuated en: velope, connecting pins extending into said envelope and protruding from one end thereof, a plurality of pairs of resistors mounted within said envelope and having substantially equal temperature coefiicients of resistance so that said resistors are of equal resistances at equilibrium temperatures, one of said resistors extending lengthwise of said envelope in substantially a straight line and being supported at one end by one of said pins and at the opposite end by another of said pins, the other resistor extending lengthwise of said envelope and being formed into a helix and being supported at one end by said firstmentioned pin and at its opposite end by another pin, said helical resistor changing resistance at a slower rate than said straight resistor with step change in current.

4. A bridge circuit .for providing a signal corresponding to rate of change of current flow in the circuit, said circuit comprising first, second, third and fourth arms having resistors formed of nickel wire, all of said resistors being of substantially equal resistance at equilibrium temperatures, the resistors in said first and second arms being in the form of a helix and of greater mass than the resistors in said third and fourth arms and the resistors in the third and fourth arms being substantially straight so that the latter resistors change resistance at a faster rate than said helical resistor with step change in current.

References Cited in the file of this patent UNITED STATES PATENTS 1,643,582 Martin Sept. 27, 1927 1,994,757 Florez et a1. Mar. 19, 1935 2,389,915 Kleirnack et a1. Nov. 27, 1945 2,440,283 Levy Apr. 27, 1948 2,463,805 Polye et al. Mar. 8, 1949 2,487,697 Conviser Nov. 8, 1949 2,528,446 McConnell Oct. 31, 1950 

